1. Technical Field
The present invention relates to a lead component and a method for manufacturing the same, and a semiconductor package, and particularly relates to the lead component suitable for being used inside a semiconductor package.
2. Description of the Related Art
A semiconductor package obtained by die bonding a semiconductor chip onto a lead frame, being a lead component, and electrically connecting a terminal section of the lead frame to an electrode of the semiconductor chip by wire bonding, and thereafter transfer molding is performed thereto using mold resin, is generally known as the semiconductor package. In die bonding, gold-silicon bonding, etc., is used in the past. However, in recent years, high-lead (Pb) solder containing nearly 90% of lead and having a melting point of about 300° C. has been frequently used, because the gold is expensive. Particularly, in a case of a product whose heat dissipation is desired to be increased, the high-lead solder is used for die bonding between the semiconductor chip and the lead frame inside of the semiconductor package. Further, in order to mount a resin-molded semiconductor package on a printed wiring board, etc., lead-tin eutectic solder having a melting point of 183° C. is used. Meanwhile, in a case of a product with little risk of heat generation, an organic film, etc., for die bonding is used in some cases.
However, regulations of environmental impact substances are promoted in each country in view of enhanced environmental consciousness, and use of lead in a solder is partially a regulation object. In order to cope with such a regulation, the lead-tin eutectic solder is replaced with tin-silver-copper solder, etc. Meanwhile, there is no replaceable bonding material in the high-lead solder used for the die bonding between the semiconductor chip and the lead frame inside of the semiconductor package, and therefore the high-lead solder has been excluded from an environmental regulation heretofore. However, lead-free tendency of a solder material is a trend of the times, and development of a lead-free high heat resistant solder material that can be applied to the die bonding of a power semiconductor chip having high heat generation, is desired.
In order to cope with such a situation, for example patent document 1 discloses a technique of a high-temperature solder having a composition of Zn—Al—Mg—Ga. Patent document 1 discloses a technique of realizing a melting point close to that of the high-lead solder, by adding Ga. Further, patent document 1 discloses a technique of using a paste-like solder. However, in the paste-like solder, cleaning after connection is generally required in many cases, and usually there is a possibility that such a paste-like solder can not be applied for general use of mounting the power semiconductor chip in which connectability can be assured without requiring any flux so as not to perform cleaning.
Further, patent document 2 discloses a solder having an optimal composition of Zn—Al.
Patent document 3 discloses a solder structure of cladding on three layers of Zn/Al/Zn, wherein wettability is improved by suppressing a formation of an Al oxide film by cladding Al with Zn, because generally a strong oxide film is formed by Al. In this solder structure, oxidation of Al is suppressed, and therefore wettability of the solder seems to be improved. However, Zn itself is a metal easily oxidized, and therefore suitable connection structure, connecting condition, and connecting apparatus need to be selected.
Further, patent document 4 discloses a technique of forming an Au layer or an Ag layer on a surface of Zn—Al based solder. This technique is the technique of suppressing oxidation of the Zn—Al based solder surface. Generally, the Zn—Al based solder is easily oxidized, and even if applying Au-soldering or Ag-soldering, soldering is applied to already partially oxidized Zn or Al, thus possibly involving an oxide at the time of connection.
As described above, conventional techniques are given as alternatives of the high-lead solder. However, all of them are given on the assumption that the solder material is individually supplied onto the lead frame, and the semiconductor chip is placed thereon to be reflowed.